Variability of surface ocean radiocarbon and stable isotopes in the southwestern Pacific

We present high‐precision radiocarbon (Δ 14 C) results and stable isotope (δ 18 O and δ 13 C) records for a coral from Heron Island (23°S, 152°E) and new stable isotope (δ 18 O and δ 13 C) records for annual coral bands from Abraham Reef (22°S, 153°E) in the southern Great Barrier Reef studied earlier Druffel and Griffin , 1993. These tracers provide unique information on the regional water mass history, and together these data allow us to constrain the variability of circulation in the upper Pacific over the past four centuries. First, we observe decreases in δ 18 O of coral from Abraham Reef and Heron Island, indicating an increase in sea surface temperature and/or a decrease in surface salinity since 1850. Second, the small Suess effect value (Δ 14 C decrease from 1880 to 1955, due mostly to fossil fuel CO 2 ) observed previously at Abraham Reef Druffel and Griffin , 1993 is confirmed in the measurements reported here from the Heron Island coral. This value is low compared to those observed in other areas of the ocean Druffel , 1997; Druffel and Linick , 1978; Nozaki et al ., 1978 between 1880 and 1955. Third, we report alterations in the correlation between El Niño events and the occurrence of low Δ 14 C, which is indicative of long‐term change(s) in circulation in the SW Pacific. The Δ 14 C shifts reported here are not large, but even small temporal changes in prebomb Δ 14 C suggest that important changes in the large‐scale state of the ocean have occurred, such as a temporal change in circulation.